While ankle foot orthoses (AFOs) are used by about 50% of children with cerebral palsy (CP) to ameliorate gait impairments, there are no systems or processes that enable a clinician to rapidly evaluate the effectiveness and limitations of an AFO, or to iterate among a selection of AFOs to determine which is most appropriate for the patient. Recent advances in powered AFO technology provide an opportunity to address this need. The long-term goal of this research is to develop and deploy a technology-based solution to prescribing passive AFOs. Light-weight, wearable, powered robotics present a path to a prescription system that can emulate the hinge characteristics of any passive AFO. The objective of the present application is to capitalize on recent advances in small, powered hydraulic systems to develop a first-generation AFO emulator. The central hypothesis driving the research is that tiny hydraulics is the best technology for an AFO emulator and that a hydraulic AFO (HAFO) emulator can be computer controlled so that in the clinical lab setting there is no difference between walking with the HAFO and walking with the traditional AFO being emulated. The reason we are undertaking this research is that through the proposed technology advances we will be taking the first steps towards moving the AFO prescription process from one based on intuition to one based on a rational process. Aim 1 of the research is to design, fabricate and bench test a pediatric-sized HAFO with computer- controlled ankle stiffness. The purpose of this aim is to produce the apparatus that is needed to determine technical feasibility of the approach. Along with realizing the HAFO, this aim will deliver a controller that causes the HAFO to behave like a rotary stiffness with adjustable spring rate. Aim 2 of the research is to perform a pilot study using five children with CP to demonstrate the capabilities of the HAFO in a laboratory environment. The hypothesis associated with this aim is that there is no significant difference in four key gait metrics when walking with the tuned HAFO emulator compared to walking with three traditional, passive AFOs of varying stiffness that the HAFO is emulating. The research described in this application is innovative because it proposes an entirely new approach to AFO prescription, which up until now has been an ad hoc process. The approach is exploratory, but has potential for moving how AFOs are prescribed in a new direction.